Catalytic polymerization process



HEAT DISTORTIIE gN TEMPE kATURE PE IZCENT MONOMEIZ IN POLISTYJZENE PERC C NT MONOM ED 0 MNDFGNEQSEF ZOHFQOPWHQ LEMI G. F. D'ALELIO Filed Sept. 28, 1948 CATALYTIC POLYMERIZATION PROCESS AVERAGE PEIZEENT CHANGEIN LENGTH IN BOILING WATER (0.5 To 2.0 PERCENT) AVERAGE PERCENT CHANGE FLOW PROPERTIES OF POLYSTTRENE A: POLYSTYRENE CONTAINING VARIOUS AMOUNTS 0F MONOMEIZ MONOMER-FREE POLTSTYRENE IN LENGTH IN BOILING WATER PERCENT MONOMED IN POLYSTTRENE PERCENT'MONOMER m A w 5 250 CONTA INING 0 T0 2.5 PERCENT BETA-BUTOXY-ETHYL STEAIZATE 2% PERCENT AVERAGE CHANGE IN LENGTH AFTER .30 MINUTES AT 10 fiazoummvw P5325 3o:

Oct. 20, 1953 Patented Oct. 20, 1953 UNITED STATES rm" OFFICE- 2;c56;3s4.. CATALYTIC POLYMERIZATIONI PROCESS-i;

Gaetano F. D.Aleli'o,. Pittsburgh, Pa., assignor to Koppers Company, Inc, a corporation of.Delaware- Application September 28, 1948 Serial.No.-a5 1,633

aryl. compounds. It also. relates. to. vinyl. aryl.

polymeric. products. having. excellent. shrink-re.- sistance... clarity, and high. resistance. to. heatdistortion.

Vinyll arylj polymers. having, substantial amounts. of residual. monomer and low-molecular-weight polymerstherein usually have certain undesirable properties. such. as, high shrinkage in boiling water, low resistancetio. heat-distortion, potential. discoloration due to oxidationof' monomer, .and,crazingdue to escape of volatile. or fugitive materials. For example, the standard grades of. polystyrene available for commercial purposes generally have. fromabQut-OA to over 1*.01 per cent by weight residual monomer. As. may be seen by astudy of Figures IandII, such amounts of. monomer are. associated with 1111-.- favorable effects on certain. thermal properties of polystyrene. Figure. 1 indicates a. relationship. of monomer, content with the. per centaverage shrinkagev in, length. of. molded polystyrene specimenscaused by. immersion, in boil- :ingwat'er (1100 (3.). ion 30 minutes. Figurell.

shows, an... association between. the amount of residual" monomer in polystyrene. andpolymerresistance to heat-distortion. Figure III" shows n the relationship otfiow properties for a, typical.

commercial, polystyrene, with its shrink. resist.-

ancelcurveA). as compared. withthe improved relationship of these, properties. in. a. lubricated.

polystyreneprepared by the process-.01 thisin vention. (curve B), which. figure is described, moreiully. hereinafter,

For theaboverindicated. reasons. there. has.

been considerable interestin. producing; substan;

tially monomer-free vinyl. aryl. polymers. the. term substantially. monomer-free) being used... herein .to. mean a monomer. content ofnotmore 11 Claims; (Cl. 260'47) thanOlLpercentflby weight, advantageously. not.

more than, 0201 percent. The. importance of) and the desire. for, such. improved polymer prod nets. are: emphasized. by. the. premium... prices Whichindustry has. been willing to payrfor mold.-v

ingcompositions. of such. materials. At present the only known methods for reducing the residual monomer content. vinyl aryl. polymers employ. expensive techniques and equipment. for.

the removal of residual. monomer. from. thepolymer products. In addition to. the, expense in volved, the products. obtained. by such. treat.- mentshavea hazy, discolored. appearance and aftercontact with.boi1ing.water. have. a rough surface, all very likely due to the method of preparation, of, processing. Moreover,. these premium products are not. available in. bead form,, which, form, has advantages in. certain applications.

Ithas. now. been i ound. that .improvedpol'ymers.

of. vinyl. aryl compounds. may be. obtained. by

employing. in. the, polymerization of vinyl aryl. compoundsa catalyst=combination consisting of.

a. benzoyl; peroxide plus .at least. one other. organic. peroxy, compound. of.the. c1ass. consisting.

of. tertiary-butyl. perbenzoate,.-. di -tertiary.-butyl.

diperphthalateand. 2,2-di-(tertiary-butylsperoxy) butane, andheating at a. temperature between. about'25? C... and about 9.5 C. until; at least. about 6.0 .percent. conversion of. monomer topolymer. has been effected and. thenheatingat.

a temperature. between aboutlOO. andabout 15.03 0,, until. substantially complete. polymerizar tion. has; been effected. Inthis. maner, polymers: are. obtained. which ..have.. excellent. resist-- ance. to. shrinkage, clarity; and, high, resistance.

to. hQQvtrdiStOTtiOH; Moreover, theuseof. plasticizers together. with, the. catalyst-combinations.

ofthis. invention. permits. the. preparation of lubricated. polymers. having. improved. relation-.- ship. between. flow. properties and, shrink. resist,- arms...

The process. of. this inventiom is. applicable to, all. vinyl aryl. compounds. and... is. particularly.

advantageous. in. the... polymerization. of styrene. The clear. polystyreneobtainedby the. practice of, this invention is a. new productwhich. mains tains. a... clarity notrattainable by substantially. monomeitrfree. pplystyrenesproduced by. prior art. methods. of, removing, residual monomer from. styrene. polymers; This. distinction. is made obvious by a. visualcomparison oi. molded pieces from. polystyrene. prepared according. to.

' the process. of, this invention with. those. from presentative samples. oi. the premiumgrade commercial; polystyrene; prepared by. other methods, the; formers being cr-ystaleclear, having.

a. light transmission. of. at least about 85.:percent of visible light through a l-centimeter thickness determined photoelectrically and compared to transmission of light through air, and the latter having a definite yellow color. In addition, the application of the present invention to suspension polymerization systems effects the preparation of beads of substantially monomerfree polystyrene, which beads have not been previously available since the prior art methods of preparing substantially monomer-free polystyrene produce the polymer in powder or other form. The substantially monomer-free, clear polystyrenes of this invention when formed into shaped articles have, upon immersion for 30 minutes in boiling water (100 C.), a change in length of less than about 7 percent, usually less than about percent, and also usually have a heat-distortion temperature of at least about 93 C.

The term a benzoyl peroxide is intended to include benzoyl peroxide and those derivatives of benzoyl peroxide having one or more chloro, bromo, fiuoro, alkoxy (i. e., methoxy, ethoxy, propoxy and butoxy), alkyl (i. e., methyl, ethyl, propyl and butyl), b-enzo, or carboperoxy groups attached to the aromatic nucleus. Such substituents may be attached to either or both of the aromatic nuclei of the benzoyl peroxide. This class includes such peroxides as chlorobenzoyl, bromobenzoyl, fluorobenzoyl, alkoxy-benzoyl, alkyl-benzoyl, phthaloyl and naphthoyl peroxides.

The use of mixtures of organic peroxy compounds as polymerization catalysts is not new in itself. Trigger-systems have been known wherein a small amount of a strongly active peroxide, such as cyclohexyl hydroperoxide, sets off a slow peroxide, such as tertiary-butyl hydroperoxide. Such systems permit the use of an otherwise slow catalyst to give the desired degree of polymerization or cure in a short time without the increase in peak temperature or exotherm otherwise necessary. More recent disclosures have shown, for use with alloxyethyl methacrylates, etc., a mixture of a relatively heat-sensitive organic peroxide, such as benzoyl peroxide, with certain relatively heat-stable peroxides, such as tertiary-butyl-hydroperoxide, ditertiary-b-utyl peroxide, l-hydroxy-cyclohexylhydroperoxide-l, etc., first at a temperature below 75 C. and then above 120 C. However, the above-mentioned catalyst-combinations have not been found satisfactory for the process of the present invention to produce substantially monomer-free vinyl aryl polymers.

The decomposition characteristics or free-radical formation of a particular peroxy compound. are usually somewhat dependent on its surroundings, i. e., on the monomer or other peroxy compound admixed with it. For example, the decomposition temperature of a peroxy compound by itself may be quite difierent from that exhibited under the influence of a monomer or other peroxy compound. Moreover, these characteristics may be varied by the type of monomer or peroxy compound. Furthermore, the selection of peroxy compounds to use in combination with a particular peroxide, such as benzoyl peroxide, may often be dependent on the type of polymerization system to be used. It has now been found, however, that the particular catalyst combinations of this invention operate very satisfactorily and may be used to produce the improved vinyl aryl polymers of this invention.

The efiective proportions of catalysts in the catalyst-combinations and eiiective proportions of catalyst-combination to monomer are dependent somewhat on the amount of residual monomer permissible in the polymer products, the specific catalyst-combination, the particular monomer or monomers, the type of polymerization system, the temperatures, the time of heat ins, and the effect of plasticizers, emulsifying agents, diluents, etc., present in the polymerization mixtures. Although the influence of many of these factors often must be determined in each particular instance, certain generalizations may be made. For example, it may be stated as generally true that low temperatures in the first heating stage over relatively long periods may permit more eificient use of the primary catalyst, i. e., the benzoyl peroxide, so that less secondary catalyst, such as t-butyl perbenzoate, etc., can be required. Moreover, the required amount of secondary catalyst can also be reduced by the use of the lowest temperatures possible in the effective range for the second heating stage over relatively long periods, thereby obtaining possibly more eificient use of the secondary catalyst than possible at higher temperatures. In addition, complete polymerization usually may be favored by a relatively high temperature at the end of the heating schedule. Thus, it is obvious that determinations of the limitation for effective ranges of catalyst ratios and catalyst-combination concentrations are difficult without specific reference to the temperatures and other conditions to be used. Moreover, the use, of the low temperatures referred to above will necessitate longer heating periods, which is an important cost factor and must also be considered in determining the conditions to be applied to any particular polymerization.

In order to make easier comparisons of the catalytic efficiencies of various peroxides, peres ters and perethers with each other and with various combinations of each other, equivalent weights of these compounds may be determined in the following manner. First, a determination is made of the equivalent weight of benzoyl peroxide or that weight required per unit weight of styrene to give, by a particular heating schedule, a polystyrene having a relative viscosity of about 2.5, e. g., from 2.40 to 2.5-5. Then the equivalent We ht of a secondary catalyst, i. e., tertiarybutyl perbenzoate, etc., is determined which will give a polystyrene of the same relative viscosity by use of the same heating schedule. Thereafter, the amounts of catalyst or mixtures of catalyst to be used for such a heating schedule can be selected according to these equivalents. For example, an -20 mixture of benzoyl peroxide and tertiary-butyl perbenzoate contains these catalysts in respective amounts having a ratio corresponding to the ratio of 80 percent of the equiva lent weight of benzoyl peroxide to 20 percent of the equivalent weight of tertiary-butyl perbenzoate. The term mixture as used herein in con nection with the catalysts in the catalyst-combinations refers to ultimate mixture in the polymerization medium in view of the fact that, although the individual catalysts are advantageously added to the polymerization system prior to or shortly after initiation of the polymerization, the secondary catalysts can be added, when convenient, any time prior to or shortly after the beginning of the second heating stage, possibly even after decomposition of most of the primary catalyst.

A previously mentioned, a determination of tho limitston ope]:ative-- amounts ot. cataiysts for: the process of this invention; is: rather: difilci-llt: because of the: numerous. factors myolyedi. H11: addition, the-lowen-li-miton the efiectiye'i ran e? foramounts: oi catalyst-combinations necessary? for the "operation: thi invention will vary as cOrdi-ngIto-the ratim oi:the:catalyststhe -corn.- binati'om, so n that a:. determimtionon" lower: limit has little meaning orvaluei Generally however; there shouldbe present: least 0.0.51... advantageouslyat least. 011*: percentof theicatar.- lyst-combi nation Moreover, in: such; catalysts combinations, the ratio of equivalent Weights of primary catalyst to secondary catalyst should-be at least about" 99%; advantageously 9&2; ion practical operation; Nevertheless, as-pointedout before, such lower limits on the secondary ca talystaredependentto-someextent orrthe -heating=- schedule employed, and, in some cases, Smaller amount of secondary catalyst are sometimes permissible with longer: heating. in one or both of the heating stages, or. with a high final temperature, Emma practical'viewpoint; the upper limit on the proportion oft secondary catalyst is determined chiefly by the cost factor. In: suspension polymerizations, however, this upper limit is also determined somewhat by the fact that the presence of the secondary catalyst in large proportions may result in poor control of the suspension polymerization and maythereby cause precipitation. or lump formation through coagulation of. polymer. beads. This is generally, avoided, however, by. catalyst .ratios greater than 30-70, 1'. e., equivalents. of benzoyllpcroxidetype' ca alyst to equivalents of secondary catalyst.

The process of this inyention is especially applicable to suspension polymerization systems. In; such systems, considerable precaution; must be: taken; to. preyentt coalescence of they globules.- ofimonomer, polymeri on-mixturesgthereoi. Suchcoalescence may" result, in? the precipitation: of;

monomenor.polymer-iromthe system. For this:

reasons it. has: generally been. found necessary, to operate suspension polymerization. systems below certain temperatures until at least a definite degree of polymerization or-conversion from monomer to polymer has been effected. For example the" case: off, styrene, the-tempera ture is: generally desirablymaintained below 95 C: until at least about pen cent conversion. to:= polymer has: been effected; Once thecon version has reached" this stage; Eh-Ev, temperature. may-' be increased with: considerably: reduced likelihood of coalescence on precipitation It: can be understood; therefore; that the activeranges of the catalyst-combinations of this. process are well suited tothe requirements or suspension polymerization systems for vinyl aryl compounds, since the first heating stage carries-- the polymerization past the sticlsyphase orthat phase of the polymerization at which the system is very" susceptible tocoalescence, and the highertemperature of the second heating stage aids" in; the completion of the polymerize-- tion after the possibility of coalescence has thus been reduced.

Although the application of the present process has been. especiallyadvantageous; in suspension. polymerization, it also efiects improvements in; producing vinyl aryl polymers by means of masssolution, and emulsion polymerizations as hereinafter illustrated in the Examples. V, VI and VII. The difiiculty in. promoting. complete: polymerization is encountered. in these. polymerization systems; as:- W311i as: in: suspension polymerization. systems, and; the process. of this;

invention is used advantageously inv effecting;- improvements. in the per cent conversion to. polymer insuoh systems.

The invention may best, described by the f 01- lowingrexamples-which are not intended as limitations-om the invention but merely to illustrate various' methods of practicing the invention. In thesev examples and throughout the specification, references to parts and percentages mean parts by weight and percentages byweight. Unless specified otherwise, the determination of monomer-content was performed. by. the ultraviolet. spectrarphotometric procedure, describ d.-

Ana ytical Chemistry 20,

312,- (1948) The standard, shrinkage or boiling, test, consists. of, immersion of. polymer samples for. 3.0-.minutes .mboiling water, a; 100 C. temperature being maintained by thev addition of sufficient salt and by continuous reflux. Ex-

cept" in the two casespointedout in Examples V and IX, the shrinkage tests were made on test" bars prepared by injection molding. The bars as molded were- 8%" x "'x but were out to 4% x X" before the'boiling test.

In whichever I ofthe fol-lowing examples suspension p'olymerizations are indicated, the suspensions were stabilized by the-useofhydroxy apatite (calcium. hydroxy hexaphosphate) as suspension agent and the procedures followed mosphere, such as nitrogen; methane, etc.

Example I E011 polym rization. xperiments were p formedi under; similar; conditions except for the ata yst: usedi. The; ou pe ymerizations were A-:.. olzpencentt.benzoylperoxide (based on weight of monomer);

B-.: 0118; percent benzoyl; peroxide plus 0.05v per.-

cent: t-butyl, perhenzo ate;

C. 02-16: percent henzoyl' peroxide plus 0.10 per.

cent-:tebutyl perbenzoate;

D; 0214,1161'081113 benzoyr: peroxide plus 0.15; percent-tzt' butyl perbenzoate; In each of the experiments styrene was polymerized in a suspension system containing:

90, parts styrene (containing dissolved catalyst) 20.0 parts distilled water 1 percent hydroxyapatite (submicronic particle siz 0.61:1 percent sodium oleate These materials, were placed in glass bottles, capped and then agitated by a rocking mechanism While the. bottles were immersed in a controlled temperature bath at C. for '7 hrs.

mer, heat-distortion and percent shrinkage. The results are as follows:

Ratio of Heat- Percent change F uiva Percent Distorin Boiling Water Run No. g Residual tion B Monomer Temp.,

C. Length Width 8-467 90-10 0. 01 94. 2 5. 93 1.47 CUP-175 80-20 0. 00 94. 1 5. 9 1. 1

Example II The procedure of Example I was repeated in four experiments using the same materials and amounts as in Example I except for the catalystcombinations which were as follow, the total amounts of catalysts in the various experiments being equivalent in peroxide efficiency:

A. 0.2 percent benzoyl peroxide (based on weight of monomer);

B. 0.12 percent benzoyl peroxide plus 0.20 percent di-t-butyl diperphthalate;

C. 0.10 per cent benzoyl peroxide plus 0.25 percent di-t-butyl diperphthalate;

D. 0.06 percent benzoyl peroxide plus 0.35 percent di-t-butyl diperphthalate.

The results of the tests on the polymer prod- The procedure of Example I was repeated in five experiments using the same materials and amounts as in Example I except for the catalyst-combinations which were as follows, the total amounts of catalysts in the various experiments being equivalent in peroxide efiiciency:

A. 0.2 percent benzoyl peroxide (based on weight of monomer) B. 0.16 percent benzoyl peroxide (BP) plus 0.04 percent 2,2-di- (tertiary-butyl-peroxy) -butane (2,2-DPB) C. 0.14 percent benzoyl peroxide plus 0.06 percent 2,2-di- (tertiary-b-utyl-peroxy) -butane;

D. 0.10 percent benzoyl peroxide plus 0.10 percent 2,2-di- (tertiary-butyl-peroxy) -butane;

E. 0.08 percent benzoyl peroxide plus 0.12 percent 2,2-di-(tertiary-butyl-peroxy) -butane;

The results of the tests on the polymer prod- A number of styrene suspension polymerizations were conducted in glass-lined, enclosed steel reactors, jacketted for compound heating and cooling, and equipped with a glass-coated impeller-agitator and upward-baflle for very efficient agitation. In each polymerization a combination-catalyst, i. e. 'benzoyl peroxide (BP) plus tertiary-butyl perbenzoate (t-BP), was used in an amount equivalent to 0.2 percent benzoyl peroxide, based on the weight of styrene. The charge in each case is as follows with the amount of catalyst indicated in the table of results given below, and with a. heating schedule of 6% hours at 92 C. and 4 hours at 114-116" C.

5500 parts styrene 4500 parts deionized-deoxygenated water 55 parts hydroxy apatite (submicronic particle size) 0.125 parts sodium sulfonate of dodecyl benzene R ti f H t Billing TgsktsPercent a 00 ea verage angein- Percent tr g The 1 onomer BP-tBP 0. Length Width Thickness PIC-4 -10 0. 00 96.1 1.4 1.9 1.8 PK-6 02-8 0. 00 95. 7 1. 9 l. 2 2. 2 PIC-8... 94-6 0. 00 95. 7 2.8 0.9 1.7 JFK-2... 96-1 0.09 95. 2 567 97-3 0.00 95.6 7.2 1.2 3.1 580. 99-1 0.18 95.0 13.9 3.1 5.9

The three experiments using catalyst ratios of 96-4, 97-3 and 99-1 could advantageously have used longer heating schedules to reduce the residual monomer content or shrinkage.

Example V Freshly distilled styrene was polymerized in bulk using benzoyl perozide (BP) alone, and benzoyl peroxide plus tertiary-butyl perbenzoate (t-BP). As indicated below in the tabulated data, the combination-catalyst was particularly effective in reducing the monomer content and shrinkage. In this case, the test bars were prepared by compression-molding rather than by the injection-molding procedure used in the other examples. Injection-molding procedures emphasize the requirement for shrinkresistant polymers since greater stresses and strains are produced in the molded articles, which increased stresses and strains result in greater shrinkages or dimensional changes on heating. On the other hand compression-molding does not produce such a high degree of stresses and strains in the molded articles and the subsequent dimensional changes produced by heat are not as pronounced as in injectionmolded articles. Therefore, as indicated below, the improvement in shrink resistance is remarkable for the articles compression-molded from polystyrene prepared by bulk polymerization according to the process of this invention.

1 Of compression-molded test bars instead of injection-molded bars.

9 of compression-molded test bals instead ioi' inj ection-molded bars.

.Example VI was placed in a glass bottle, capped, and ag'iv tated by a rocking-mechanismwhile immersed in a temperature-controlled oil bath at 90 C. for 7 hours and at 115 C. for 3 hours. The results are tabulated-below:

Percent catalyst Ratio of No. 3 dents Sion BP 1 tBP BP-tBP (A) 75's .j. 100-0 2536 (B) 759 0.16 '0. 10 -'802O =37. '1

More :complete conversion can be .efiected by the use of more favorable .temperaturesand heating schedules with the combination-catalysts.

Example V! I This example shows :a 10 percent improvement in the .reduction of residual monomer ;con tent for polymers produced by the emulsion polymerization .of styrene using equivalent amounts of benzoylperoxide (BP),::and benzoyl peroxide pl-us tertiary-butyl i 'ierbenzoate (tBP). The procedurefollowed wassimilar to that used in :Example I except that a heating schedule .of 3 hours at 70 Grand 3 hours-at 100 .C.' was\employed and the polymerization mixture had the cafes theisp'ectoplriotometric analysis'ziioriresidual monomer, 1a comparison "was made of the percent methanol-soluble material present in the polymer products. Theinumeric'al value ioripercent methanol-solubles is usually higher than the spectographic value for percent residual monomer. The data indicate the :low methanol- -soluloles content, and the excellent shrink-resistanceand heat distortion-temperatures of the c'opolym'er products.

"Monomer Gomp'osi-i BoilingTesta "on I I Percent Change Mcth- Heat Run No. P seingll IIPist.

Percent ercent o u as em'p. V H o-Gl- Length Width Sty1 ene Styrene co no- '-0.-'-74 95. 7 57 5 .25; 5-1. 14; 94.6 36 54' 0:09 92.22 75 -o.o0- 9635 -Ea:ampZe.IX

"Tw'o copolymers of styrene and diethyl litumarate were prepared by the suspension polymerization procedure of 'Example I. In place'of styrene, B0 parts of "a 'Jmixture was used "which mixture consisted of 95 percent styrene and 5 percent 'diethylfum'arate. "The amounts of catalystused areequivalent'and 'asi'ndieated inth'e table below.

The're'ductionin percent methanol-solubies eifected by the'proc'ess of thisiinvention is indicated'by comparison of the Value *forpolymer (B) with "that for 1 (A) The shrink resistance is correspondingly improved. As in Example "V, the shrinkage tests were conducted on compression molded bars and the same "qualifications apply with regard -to evaluating the shrinkage data "as described in Example V. The data for the 'copolymers are "summarized in the following table.

following composition.

. v i Ratio-of aPercen't v Per- Pei- P "ce t 40 p r s y q RN? cent cent .1 5 9 5 lv Sh i nk ge '60. parts distilled water I 31 .tBP i 5 5 inL'ength bp'artssodiumsulfonate of'do'de'cyl benzene I h n v l i r (A)..- 762 0. 2t, "nun 5,70. 27. The data are-a5 follow. (B). 761 .0. l6 0.10,. 80-20 0. 70 1.77

L: pyememycatw1 Oicompressmn-moldedtest bars. .l r t Ratlooi T fit "Run; ys =-Equi-va- .1 H

No. I "ienns'er: Example X 11 :BP {BP 2. itBP onomer V 1 A copolymer of styrene and acrylonitrile was A 772 p 0 10030; "1 B0 prepared by suspension polymerization according BQIIIIIIIIIIIII 771: 10.1l6 afia $-20. 4:18 170 the p ocedure of Example-I, using 0.16 per- I cent benzoyl peroxide plus 0.10 percent t'ertiary- .Eou-r copolymers :of styrene and ortho-chloi'ostyrene were prepared by the suspension ?polymerization procedure of Example .-I, :using 0.16 percent .benzoyl peroxide plus 0.10 percent .tertiary-butyl gper-benzoate. for each polymerization.

In place of the styrene usedin Example I,

parts of various mixtures of styrene vandorthochloro-styrene were =used. The .aproportions of styrene and =ortho-chloro-styrene in these mixtures :are indicated below .in *the tabulated data.

,Since the presence of a .comonomer 'complibutyliperbenzoate. In placeofithe styrene used in Example "I, .90 :parts of a.mixture was used, which mixture-contained 90 percent-styrene and ID-percent --acrylonitri1e. The :resultant co'polymer l'i-ad a boiling water shrinkage of 5.0 7 percent *in length.

As'may be seen rfrom the above examplespconditions especially isuitable .for the-suspension poly- 11 The following table indicates the actual weight percentages of the catalyst-combinations used for various catalyst ratios in various concentrations renes, fluorostyrenes, vinyl chloro-naphthalene, p-chloro-p'-vinyl-diphenyl, etc.; hydrocarbon groups, such as alkyl, alkenyl, aryl, aryl-alkyl,

given as benzoyl peroxide (BP) equivalents. alkyl-aryl, cycloaliphatic, etc., for example,

Ratio 0.05% BP plus 0.10% BP plus- 0.20% BP plusof EquivatBP or or tBP or or tBP or or 1611 DtBP 2,2DPB DtBP 2,2DBP BP DtBP 2,2DPB

Thus, for an equivalent of 0.05 percent benzoyl peroxide, there should be present at least 0.006 percent benzoyl peroxide and at least 0.0013 actual weight percent of tertiary-butyl perbenzoate based on the weight of monomer, the total weight of the catalyst-combination being equivalent to 0.05 percent benzoyl peroxide. For an equivalent of 0.10 percent benzoyl peroxide, there should be present at least 0.03 percent benzoyl peroxide and at least 0.0025 percent tertiarybutyl perbenzoate, the total Weight of the catalyst-combination being equivalent to 0.10 percent benzoyl peroxide based on the weight of monomer.

Generally the lower limit for the temperature range of the first heating stage is that temperature at which the benzoyl peroxide type catalyst will promote an appreciable rate of polymerization under the influence of monomer and other peroxy compounds, and under other conditions of polymerization. While benzoyl peroxide will usually catalyze vinyl aryl polymerizations at room temperature, or about C., the rate of polymerization generally is not sufi'icient to be very practical until a temperature of about 0., or more advantageously 0., is reached. Many of the substituted benzoyl peroxides have lower decomposition temperatures than benzoyl peroxide itself and can usually be employed to good advantage in promoting polymerizations at temperatures of 25 C. or higher. It has been found that the catalyst-combinations of this invention operate satisfactorily in a temperature range of about 25-95 C. for the first heating stage, advantageously about 50-95 C. when benzoyl peroxide itself is used. For the second heating stage a temperature range of about 100-150 has generally been found suitable. As pointed out before, however, there are numerous factors which may effect the polymerizations; and since it is, therefore, diificult to set the temperature limits without some indication of the other conditions involved, it must be understood that the temperature limits may vary somewhat according to these conditions.

The vinyl aryl compounds which may be used in the practice of this invention include styrene, vinyl naphthalenes, etc., and their substitution products. Hereinafter, reference to substituted vinyl aryl compounds is intended to mean vinyl aryl compounds which have substituents replacing hydrogen of the aryl nucleus rather than hydrogen of the vinyl side chain. The substituted vinyl aryl compounds may include those having one or more of the following substituent groups: halogen, such as chloro, fiuoro, etc., for example, monochloro-styrene, i. e., ortho-, metaand parachloro-styrenes, dichloro-styrenes, trichlorostye methyl-styrenes, such as monoand dimethyl-' styrenes, e. g., para-monomethyl-styrene, 3,4-dimethyl-styrenes, etc., ethyl-styrenes, isopropylstyrenes, vinyl methyl-naphthalenes, divinyl benzenes, partial polymers of divinyl benzene, phenyl-styrenes, phenethyl-styrenes, tolyl-styrenes, cyclohexyl-styrenes, etc.; cyano, for example, monoand dicyano-styrenes; substituted alkyl groups, such as trifiuoromethyl, cyanomethyl, alkoxyalkyl, carboxyalkyl, etc., for example, trifluoromethyl-styrenes, cyanomethyl-styrenes, methoxymethyl-styrenes, acetoxyethylstyrenes, etc.

These vinyl aryls may be polymerized, according to the process of this invention, alone, in mixtures containing one or more vinyl aryls, or with one or more other copolymerizable ethylenic compounds. Where styrene or another vinyl aryl compound is copolymerized with a copolymerizable ethylenic compound other than a vinyl aryl compound, it is sometimes advantageous that the vinyl aryl compound be in preponderance, especially when the copolymerizable ethylenic compound is one usually slightly reluctant to copolymerize with styrene or Vinyl aryl compound. The preparation of vinyl aryl copolymers by the process of this invention is illustrated by the above Examples VIII. IX. and X.

nitrile derivatives of acrylic, methacrylic, chlo-,

roacrylic, beta-cyano-acr onitrile, methacrylonitrile, chloroacrylonitrile, fumaronitrile, etc.; methylene-malonic esters, the mono alkyl esters and the dialkyl esters, e. g., the monomethyl and the dimethyl esters, the dipropyl esters, etc.; allyl derivatives, e. g. acrolein, methacrolein, allyl methyl ketone, allyl ethyl ketone, allyl chloride, allyl methyl ether, allyl ethyl ether, allyl phenyl ether, allyl acetate, allyl propionate, allyl acrylate, methallyl acrylate, diallyl phthalate, diallyl oxalate, diallyl succinate, diallyl ether, diallyl ketone, dimethallyl ketone, etc. maleic, fumaric, citraconic esters, e. g., di-

ylic acids, e. g., acrylmethallyl ethyl ether,

recesses methyl malez ite, dimethyl fumarate, diethyl maleate, diethyl fumarate, :diisopropyl :maleate, dimethyl citraconate, dethyl citraconate, 'etcz; vinyl ethers, e. g. divinyl ether, vinyl methyl ether, vinyl :p'henyl ether, .etc.; vinyl keton'es, e. g.,-diviny1 ketone, vinyl methyl 'ketone, acrylophenone, etc. The vinyl aryl or mixtures f vinyl 'aryls 'may becopolymerized with any "copolymerizable ethylenic monomer such as the above or with a mixture "containing tany ber of'suc'h monomers.

The process of this invention has been found especially useful in the preparation of plasticized 'or lubricated polymers. "Normally the presence of a plasticizer in a polymer causes an increase in the -s'hr-inkage and a lowering of the "heatdistortion temperature. However, the improvements in these thermal properties effected by the present invention make "itpossible to produce plasticized or lubricated *vinyl and polymers having a resistance to shrinkage and to heat-distortion comparable 'to that heretofore found only in non-plasticized vinyl -aryl polymers.

The distinction between plasticizers and lubrican-ts for polymers is not always very clear. Generally plasticizers have more of a solvent or softening effect on polymers andcause-greater changes in the physical propertiesge. *g., Eductility, flexibility 'andimpact'strength, than lubricants do. 0n the otherhand, lubricants eare used-to improve the ease of molding and toaid mold release. "Since there is considerable overlapping of the particular function of a great many compounds used topromote ease of flow, and in order to facilitate reference "to these compounds, the term plasticizer is used broadly hereinafter to include both plasticizers and lubricants.

The improvements effected by the use of *plasticizers in accordance with the practice of the present invention are illustrate'din the following-examples. Inthese examples and throughout the specification, flow means the number of secondsa polymer sample requiresto'flow 155 inches at 135 C. and 1000p. s. i. through a vertical orifice having a diameter of and a length of 1 The apparatus used in determining the flow is described by the American Society for Testing Materials in specification D569-44T.

Example XV Azseriesof suspension *polymerizations of styrene were conducted according to the procedure of Example'I using the catalyst-combination'of run C and various percentages of beta-butoxy ethyl stearate based on the .monomer weight. The resultsfrom these polymerizations are summarized in the following table.

"Example XVI Example XV was repeated using butyl stearatein place (if beta butOXy-ethyl stearate. The results are given-in the following table.

Boiling a'Butyl r Average Heat Tests, Run ,No. .S tearate Flow Dist. Percent (Percent) j (Seconds-y Temp.,0. Change, Lengt Furthermore, improvements in the relationship of flow properties of a'plasticized polysty-- rene to its shrinkage in length, as eiT-ected by practice of the present invention, are made apparent "by'an examination of Figure III. Figure III shows the relationship between "flow properties and percent shrinkage in length "for:

A.. Polystyrene containing various amounts .of

residual monomer (0.3 to 2.0 percent) B. -;Substantial1y .monomer-free polystyrene of the .present invention containing 0 to 2.5% .beta butoxyeethyl .stearate.

T-hus the'curves show that, where it is desired to have a polystyrene having aflow of seconds, such --a polymer prepared by the present invention, using butoxyethyl stearate as plasticizer, would have an average shrinkage in length of about 115 percent (curve B), whereas a polystyrene having the same flow without plasticizer and as formerly prepared would have an average shrinkage 'in'length of about 27 percent.

It is obvious, therefore, that the present-invention'permits'a greater flexibility in the properties of vinyl aryl polymers than was formerly possible. For example, whereas it was formerly necessary to sacrifice resistance to shrinkage andto heat distortion in order to produce a lubricated 'or plasticized polystyrene having especially good flow properties, it is possible now by the practice of this invention to prepare a plasticized polystyrene having a resistance to shrinkage and to heat distortion approximating that of the present standard commerical grade polystyrene butalso having especially good flowing properties. Thus the flow properties of the plasticized polystyrene prepared by the practice of this invention may approximate the good flowing properties of the plasticized, highshrinkage, high heat-distortion palystyrene heretofore produced. Actually therefore, the present process permits the preparation of a plasticized polystyrene having much better resistance to shrinkage, approximately as good or better resistance to heat distortion and vastly improved flow properties than the standard, unplasticized polystyrene now commercially available.

Moreover, the preparation of plasticized or lubricated polymers by .the practice of this invention permits the addition of plasticizer or lubricant to the polymerization mixture before or duringthe early stages of the polymerization. Other methods of preparing substantially monomer-free polymers are not so advantageously suited to the addition of plasticizer or lubricant to the polymerization mixture, since later treatments for removal of monomer can remove all or part of the plasticizer or lubricant.

Various types of plasticizers are suitable "for use in the practice of this invention. Included among these are: fatty 'acid "ester plasticizers, such as bu-tyl stearate, beta-butoxyethyl=stearate,

methyl oleate, amyl oleate, cyclohexyl stearate; esters of dicarboxylic aliphatic acids, such as dicapyryl sebacate, etc.; aryl ether and ester plasticizers such as dimethyl phthalate, dibutyl phthalate, diamyl phthalate, dibenzyl maleate, beta-phenoxyethyl benzoate, beta-(3-chloro-2- xenoxy)-ethyl levulinate, beta-ethoxyethyl 2- chlorophenoxy acetate, beta lbutoxyethyl phenoxy-acetate, diaryl ether derivatives such as chlorinated diphenyl ether and cyclohexyl chlorinated diphenyl ether, aryloxyalkyl fumarates, such as beta-phenoxyethyl fumarate; triaryl phosphates, 1,3 di 4 tertiary butyl phe noxy)isobutane, ethyl lactate salicylate, styrene glycol diesters, etc.; hydrocarbon plasticizers such as diphenyl and alkylated derivatives, alkylated naphthalenes, polyisobutylene, polymers of alpha-methyl-styrenes, dimers and trimers of styrene, etc. chlorinated hydrocarbon plasticizers such as chlorinated waxes, chlorinated diphenyl, chlorinated naphthalene, 1,2- bis(4-chloro-phenyl) ethane; and various other types of plasticizers which are compatible with the vinyl aryl polymers and which do not act to inhibit or appreciably retard the polymerization. The amount of plasticizer to be added usually depends on a number of factors, which include the eliiciency of the particular plastioizer, the degree of plasticity desired, etc. In general, however, at least about 02-05% plastioizer is added before any noted change in flow or plasticity is accomplished.

While it is believed that the improvements in shrink resistance and heat distortion of vinyl aryl polymers made possible by the process of the present invention may be associated with the substantial absence of monomer in these polymers, it is not intended that the scope of the invention be limited in such a manner. Since it is possible that the improvements in thermal properties can be inherent in the process of preparing the polymers and that the absence of monomer can be merely incidental to the accomplishment of these improvements in thermal properties, it is intended that the scope of the invention is more aptly described and claimed according to the process for preparing the polymers as disclosed and claimed herein.

What is claimed is:

1. The process of polymerizing a polymerizable mass comprising a vinyl aryl compound intimately mixed with a catalyst-combination consisting of 2,2-di-(tertiary-butylperoxy) -butane and a benzoyl peroxide or" the class consisting of benzoyl peroxide and its chloro, bromo, fluoro, alkoxy, alkyl, benzo and carboperoxy nuclear-substituted derivatives by heating the polymerizable mass at -95 C. until at least about percent conversion to polymer has been effected, and subsequently at 109-Il50 C. until substantially complete polymerization has been effected.

2. The process of polymerizing a polymerizable mass comprising a vinyl aryl compound intimately mixed with a catalyst-combination consisting of benzoyl peroxide and 2,2-di-(tertiary-butyl peroxy) -butane by heating the polymerizable mass at 5=-95 C. until at least about 60 percent conversion to polymer has been effected, and subsequently at 100-l50 C. until substantially complete polymerization has been efiected.

3. The process of claim 2, in which the polymerization is conducted in a suspension polymerization system.

4. The process of claim 2, in which the polymerizable mass also contains a plasticizer.

' 5. The process of claim 2, in which the vinyl aryl compound has an alkyl group substituted on the ring.

6. The process of polymerizing a polymerizable mass comprising styrene intimately mixed with a catalyst-combination consisting of benzoyl peroxide and 2,2-di-(tertiary-butyl-peroxy) -butane by heating the polymerizable mass at 5095 C. until at least about 60 percent conversion to polymer has been effected, and subsequently at l00-l50 C. until substantially complete polymerization has been effected.

7. The process of claim 6, in which the polymerization is conducted in a suspension polymerization system.

8. The process for the suspension polymerization of styrene comprising the steps of heating an aqueous suspension of styrene at approximately to C. for at least six hours and subsequently heating at approximately to 116 C. for at least three and one-half hours, said styrene suspension containing a peroxy-catalyst mixture comprising at least about 0.03 percent benzoyl peroxide and at least about 0.0025 percent 2,2 di (tertiary butyl peroxy) butane, the total percentage of peroxy-catalysts being at least equivalent to 0.1 percent benzoyl peroxide, and the percentages of pcroxy catalysts being based on the weight of styrene.

9. The process for the suspension polymerization of styrene comprising the steps of heating an aqueous suspension of styrene at approximate- 1y 90 C. for at least six hours and subsequently heating at approximately 1l2-116 C. for at least three and one-half hours, said styrene suspension containing a peroxy catalyst mixture comprising approximately 0.18 percent .benzoyl peroxide and approximately 0.05 percent 2,2-di- (tertiary-butyl-peroxy)-butane, the percentages of peroxy catalysts being based on the weight of styrene.

10. The process of copolymerizing a vinyl aryl compound with at least one other coploymerizable ethylenic compound in the presence of benzoyl peroxide and 2,2-di-(tertiary-butyl-peroxy) -butane by heating the polymerization mixture at 50-95 C. until at least about 60 percent conversion to polymer has been efiected and subsequently at 100-150 C. until substantially complete polymerization has been effected.

11. The process of claim 2 in which the vinyl aryl compound has achloro group substituted on the ring.

GAETANO F. DALELIO.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Perry et al., Article in Modern Plastics, Nov. 1947, pages 134-136, 216, 218, 220 and 222. 

1. THE PROCESS OF POLYMERIZING A POLYMERIZABLE MASS COMPRISING A VINYL ARYL COMPOUND INTIMATELY MIXED WITH A CATALYST-COMBINATION, CONSISTING OF 2,2-DI(TERTIARY-BUTYLPEROXY)-BUTANE AND A BENZOYL PEROXIDE OF THE CLASS CONSISTING OF BENZOYL PEROXIDE AND ITS CHLORO, BROMO, FLUORO, ALKOXY ALKYL, BENZO AND CARBOPEROXY NUCLEAR-SUBSTITUTED DERIVATIVES BY HEATING THE POLYMERIZABLE MASS AT 25*-95* C. UNTIL AT LEAST ABOUT 6- PERCENT CONVERSION TO POLYMER HAS BEEN EFFECTED, AND SUBSEQUENTLY AT 100*-150* C. UNTIL SUBSTANTIALLY COMPLETE POLYMERIZATION HAS BEEN EFFECTED. 